Re: [PATCH v2 1/3] nvmem: core: improve range check for nvmem_cell_write()

From: Jennifer Berringer
Date: Tue Oct 29 2024 - 17:31:21 EST


On 10/29/24 13:55, Srinivas Kandagatla wrote:
> if (!nvmem || nvmem->read_only || len != cell->bytes)
>     return -EINVAL;
>
> Does this work?
>
> --srini

I decided against this because it seems potentially useful to allow len to be less than cell->bytes when bit_offset is nonzero. I assumed that was the purpose of the original "cell->bit_offset == 0".

For example, if a cell entry has the following field values
{ .bit_offset = 4, .nbits = 8, .bytes = 2, ...}
then it would make sense to call nvmem_cell_write() with len=1 in order to write 8 bits. To allow that, I used "len > cell->bytes" instead of "!=" later in this function:

>> @@ -1780,9 +1779,13 @@ static int __nvmem_cell_entry_write(struct nvmem_cell_entry *cell, void *buf, si
>> return -EINVAL;
>> if (cell->bit_offset || cell->nbits) {
>> + if (len > cell->bytes)
>> + return -EINVAL;
>> buf = nvmem_cell_prepare_write_buffer(cell, buf, len);
>> if (IS_ERR(buf))
>> return PTR_ERR(buf);
>> + } else if (len != cell->bytes) {
>> + return -EINVAL;
>> }

If you disagree with my reasoning then yes, your suggestion works and I can use that instead of what I wrote. None of the current in-tree callers of this function rely on that possibility I described.

Thank you for the feedback.

-Jennifer